BestTimeToBuyAndSellStocks.java

package dynamic_programming;

/**
 * Created by gouthamvidyapradhan on 17/03/2017.
 Say you have an array for which the ith element is the price of a given stock on day i.

 If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

 Example 1:
 Input: [7, 1, 5, 3, 6, 4]
 Output: 5

 max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
 Example 2:
 Input: [7, 6, 4, 3, 1]
 Output: 0

 In this case, no transaction is done, i.e. max profit = 0.
 */
public class BestTimeToBuyAndSellStocks
{
    /**
     * Main method
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception
    {
        int[] prices = {1, 1, 1, 1, 1};
        System.out.println(new BestTimeToBuyAndSellStocks().maxProfit(prices));
    }

    public int maxProfit(int[] prices)
    {
        if(prices.length == 0) return 0;
        int[] max = new int[prices.length];
        max[prices.length - 1] = prices[prices.length - 1];
        for(int i = prices.length - 2; i >= 0; i --)
        {
            max[i] = Math.max(prices[i], max[i + 1]);
        }
        int result = Integer.MIN_VALUE;
        for(int i = 0, l = max.length; i < l; i ++)
        {
            result = Math.max(result, max[i] - prices[i]);
        }
        return result;
    }
}